What we know about the Las Vegas shooter's girlfriend Marilou Danley

Investigators are busy reconstructing his life, behaviour and the people he encountered in the weeks leading up to the deadliest mass shooting in modern USA history, FBI Deputy Director Andrew McCabe said.

Federal Bureau of Investigation agents met Danley when she got off her flight from the Philippines Tuesday and the sheriff said she was "a person of interest" in the case, according to the Associated Press.

Danley, considered a "person of interest" in the case, was out of the country in Asia at the time of the shooting, having traveled to Hong Kong and Manila in the days before Paddock's attack.

"He never said anything to me or took any action that I was aware of that I understood in any way to be a warning that something like this was going to happen".

The man accused of gunning down 58 people from a perch high up in Las Vegas'Mandalay Bay Resort and Casino had cameras set up inside and outside of his hotel room, authorities said Tuesday.

Both the police and Danley's sister have helped piece together the circumstances that led to her being overseas when Paddock killed at least 59 people and injured more than 500 more.

Paddock had 23 firearms at his disposal in his hotel room. Police said they believed he had used 10 suitcases to smuggle the weapons up to the room.

ABC Newsreports that a total of 42 weapons were found between the hotel room and Paddock's Mesquite and Reno properties, two being modified from semi-automatic to fully automatic. "She was away so that she will not be there to interfere with what he's planning".

Police confirmed this evening that they found several pounds of ammonium nitrate - a material used to make explosives - inside the suspect's auto.